A transmission disclosed in JP2002-139146A, which will be hereinafter referred to as Reference 1, includes a synchromesh mechanism in which a sleeve is slid in an axial direction so that the sleeve is spline-connected to a clutch ring while rotations of the sleeve and the clutch ring are synchronized with each other. As a result, a desired gear range is achieved. A shift actuator including a rotation motor and a gear mechanism is used as a driving source of the synchromesh mechanism.
A clutch apparatus disclosed in JP2010-96190A, which will be hereinafter referred to as Reference 2, includes a dog clutch mechanism in which a sleeve and a clutch ring are provided. High teeth and short teeth are formed at an inner periphery of the sleeve in a state where a radial height of each high tooth and a radial length of each short tooth are different from each other. Clutch forward teeth and clutch rearward teeth are formed at an outer periphery of a protrusion portion of the clutch ring. The number of clutch forward teeth is smaller than the number of clutch rearward teeth. In addition, the clutch forward teeth and the clutch rearward teeth are displaced one another in an axial direction. The height of each clutch forward tooth, i.e., a radial length of the clutch forward tooth, is defined so that the clutch forward teeth engage with the high teeth but not to engage with the short teeth of the sleeve. The height of each clutch rearward tooth, i.e., a radial length of the clutch rearward tooth, is defined so that the clutch rearward teeth engage with the short teeth of the sleeve. Then, a clutch groove for the high teeth, which will be hereinafter referred to as a high tooth clutch groove, is formed between the clutch forward tooth and the clutch rearward tooth so that the high tooth of the sleeve is engageable with the high tooth clutch groove. In the same way, a clutch groove for the short teeth, which will be hereinafter referred to as a short tooth clutch groove, is formed between the clutch rearward teeth adjacent to each other so that the short tooth of the sleeve is engageable with the short tooth clutch groove.
In a case where the sleeve is slid in the axial direction, the high tooth makes contact with an end surface of the clutch forward tooth, and thereafter enters between the clutch forward teeth to make contact with a side surface of the clutch rearward tooth. As a result, a phase adjustment is completed. The sleeve is then further slid in the axial direction so that the high tooth engages with the high tooth clutch groove while the short tooth engages with the short tooth clutch groove. As a result, the sleeve and the clutch ring are completely in engagement with each other.
According to the synchromesh mechanism disclosed in Reference 1, a pressing friction force is used, which leads to a high output of the shift actuator. In addition, because the gear mechanism is used for the shift actuator, a breakage of a gear, for example, is caused by an impact at a shifting operation. Further, a drag may occur in a case where the synchromesh mechanism is not operated, which may be a cause of power loss and deterioration of fuel economy.
According to the dog clutch mechanism disclosed in Reference 2, an issue caused by the synchromesh mechanism does not occur, Nevertheless, the short tooth clutch groove is formed so that the short tooth is engageable with the short tooth clutch groove but the high tooth is inhibited from engaging with the short tooth clutch groove. Therefore, until the high tooth reaches the high tooth clutch groove and the rotations of the sleeve and the clutch ring are completely synchronized with each other, the sleeve and the clutch ring are inhibited from being completely in engagement with each other. As a result, a shifting time may be elongated.
A need thus exists for a dog clutch for an automated transmission which is not susceptible to the drawback mentioned above.